Generally, an inkjet printhead is an apparatus that is used to produce or form an image, such as an image having predetermined colors, for example, by discharging or ejecting small ink droplets on image locations on a printing medium. Such an inkjet printhead can generally be classified as one of two types of inkjet printheads based on die discharging mechanism that is used to eject the ink droplets. A first type is a thermal inkjet printhead in which ink droplets are ejected by a tension or pressure that is produced from ink bubbles that are generated by a heating source. A second type is a piezoelectric inkjet printhead in which ink droplets are ejected by a pressure that is applied to the ink from the deformation of a piezoelectric material or element.
By way of an example, a mechanism for discharging or ejecting ink droplets in the thermal inkjet printhead is described in more detail below. When a pulse current flows through a heater, such as a heater made of resistive heating elements, for example, heat is produced by the heater and the ink that is adjacent to the heater can be heated up to about 300 Celsius (° C.) quite rapidly. When as a consequence the ink boils, ink bubbles are produced and as the ink bubbles expand they apply pressure to the ink that fills the ink chambers. As a result, the ink in the ink chamber that is near a nozzle is ejected in the form of ink droplets to a region outside of the ink chamber.
The thermal inkjet printhead can have a configuration or structure in which a nozzle layer and a chamber layer are stacked or disposed on a substrate, with the chamber layer being disposed on the substrate and the nozzle layer being disposed on the chamber layer. The substrate can support multiple heaters. The chamber layer can include multiple ink chambers and the nozzle layer can include multiple nozzles. Each of the ink chambers in the chamber layer can be configured to be filled with ink that is to be ejected for printing. Each of the nozzles in the nozzle layer can be configured to eject ink that is contained in an associated ink chamber. In thermal inkjet printheads, the ink's physical properties, such as viscosity, for example, can change when the operating temperature of the thermal inkjet printhead changes. Because of the change in the ink's physical properties caused by the changes in operating temperature, the uniformity with which ink droplets are ejected across the thermal inkjet printhead can deteriorate, causing the quality of the printed image to be less than desirable.